Question

so I have this problem. My Database has two tables that look something
like this:

    Table A:

    ============================
    Username     Group Number
    ============================
    mike              1
    john              1
    stan              2
    mark              2

    ============================


    Table B:

    ========================================
    Username     FeatureA  FeatureB FeatureC
    ----------------------------------------

    mike           Yes                Yes
    john                      Yes
    stan                      Yes     Yes
    mark           Yes                Yes
    ========================================

Tables A and B are joined together by Username and I need something that looks like this:

    ============================================
    Group Number  FeatureA   FeatureB   FeatureC
    ============================================

         1         1            1          1
         2         1            1          2
    ============================================

Basically I need to count the number of users in each group that have access to each feature.

Answer 1

Try this

SELECT a.`Group Number`, 
       SUM(CASE b.FeatureA WHEN 'Yes' THEN 1 ELSE 0 END) AS FeatA, 
       SUM(CASE b.FeatureB WHEN 'Yes' THEN 1 ELSE 0 END) AS FeatB, 
       SUM(CASE b.FeatureC WHEN 'Yes' THEN 1 ELSE 0 END) AS FeatC 
FROM tableA a JOIN tableB b
ON a.username = b.username
GROUP BY a.`Group Number`